The field of the disclosure relates generally to the growing of nanotubes, and more specifically, to an augmented reactor for chemical vapor deposition (CVD) of ultra-long carbon nanotubes (CNTs).
Carbon nanotubes are small tube-shaped structures essentially having a composition of a graphite sheet in a tubular form. Carbon nanotubes feature diameters less than 100 nanometers, and large aspect ratios, where the length is much greater than is the diameter. For example, a length of the CNT may be more than 1000 times the diameter. CNTs are semiconducting or highly conducting, depending on their chirality. Such features make carbon nanotubes ideal for a multitude of electronic applications.
Generally, carbon nanotubes can be classified into single-wall type and multi-wall type. A single-wall type carbon nanotube structure has only one cylindrical graphitic layer. A multi-wall type carbon nanotube structure has two or more nested cylindrical graphitic layers.
Existing linear chemical vapor deposition (CVD) reactors are capable of growing carbon nanotubes either perpendicular to the feed gas flow or aligned along the direction of the feed gas flow. Perpendicular growths are limited in height to the size of the tube defined by the furnace in which the CNTs are grown, usually one, two, or four inches. Growth aligned with the feed gas flow direction is limited in length to the size of the region within the furnace over which the temperature remains constant.
Tube furnaces currently used for linear CVD reactors are approximately four feet in length. The ends of the reactor tube protrude from the furnace such the temperature is not constant near the ends of the furnace. The center of the furnace contains a region of constant temperature. In CVD CNT growth, the feed gas is heated to a certain temperature, which takes some time, and since the feed gas is flowing, takes some distance. This distance is longer than the cooler region at the beginning of the CVD reactor tube. Only the region beginning from where the gas is sufficiently heated to an ending point of this constant temperature region in the tube furnace can be used for nanotube growth.
The longest nanotubes grown to date in such tube furnaces are approximately 18.5 cm in length. The growth terminated at this length because the chamber temperature decreased approximately 18.5 cm past the growth substrate.
One solution for the production of longer nanotubes would be to use a longer straight (linear) CVD reactor in a longer furnace. However, the length of tube produced is still limited by the length of furnace and the CVD reactor tubes available, and thus nanotubes of arbitrary length cannot be fabricated.